The present invention relates to a rotor control system for a rotary-wing aircraft, and more particularly to an upper rotor control system for a counter-rotating rotor system.
Control of a rotary-wing aircraft is affected by varying the pitch of the rotor blades individually as the rotor rotates and by varying the pitch of all of the blades together. These are known respectively as cyclic and collective pitch control. Blade pitch control of a rotary wing aircraft main rotor is typically achieved through a swashplate assembly which transfers the motion of non-rotating control members to the rotating members.
The swash plate assembly is typically concentrically mounted about a rotor shaft. The swash plate assembly generally includes two rings connected by a series of bearings with one ring connected to the airframe (stationary), and the other ring connected to the rotor hub (rotating). The rotating ring is connected to the rotor hub through a pivoted link device typically referred to as “scissors”, with the static ring similarly connected to the airframe. The rotating swash plate rotates relative the stationary swash plate. Apart from rotary motion, the stationary and rotating swash plate otherwise move as a unitary component.
Collective control is achieved by translating the swash plate assembly up and down with respect to the rotor shaft and cyclic control is achieved by tilting the swash plate relative to the rotor shaft. The stationary ring is typically mounted about the rotor shaft through a spherical ball joint or uniball that allows for tilt of the swash plate assembly, with the standpipe surrounding the rotor shaft allowing translation of the swash plate assembly along the axis. The pitch links connect the rotating ring of the swash plate assembly to the pitch or control arms of the rotor blades. The stationary swash plate assembly of the swash plate assembly is positioned by servos which are actuated in response to the pilot's control signals. Thus, when the pilot inputs a control command, the stationary swash plate assembly is raised, lowered or tilted and the rotating swash plate assembly follows to impact collective and cyclic pitch control to the rotor disc.
A rotary wing aircraft with a counter-rotating rotor system requires an upper and lower rotor control system. Modern flight control systems may also control the upper rotor system independent of the lower control system so as to provide increased fidelity of aircraft control. The lower rotor system typically utilizes a relatively conventional swashplate arrangement mounted about a lower rotor shaft while the upper rotor system utilizes a relatively more complex upper rotor control system mounted through the upper rotor shaft which counter-rotates relative the lower rotor shaft. The upper rotor control system includes an upper rotor swashplate assembly, a motion multiplier, and long control rods, located inside the upper rotor shaft. Buckling stability of the long rods requires a relatively heavy, large diameter solution which may be difficult to package within the rotor shaft.
Accordingly, it is desirable to provide a compact, light-weight upper rotor control system for a counter-rotating rigid rotor system.